UUID and Drive Cloning

Question

When cloning a drive (using dd), will the UUID's for each partition change, or are they hardware specific? or does cloning it preserve the UUID as well?

What happen if a system detected two devices with the same UUID?

Solution

UUIDs are not hardware-specific but stored in the partition's filesystem. That means cloning a disk or partition with dd will result in the same UUID.

You can assign a new UUID by using:

• tune2fs -U random <device> (ext2/ext3/ext4)
• xfs_admin -U generate <device> (xfs)
• reiserfstune -u $(uuidgen) <device> (reiserfs)
• mkswap -U $(uuidgen) <device> (swap)

Having duplicated UUIDs doesn't necessarily lead to errors. However booting and mounting a device by UUID will become ambiguous and may lead to the wrong device being used.

Comments

[Ƭᴇcʜιᴇ007]

Why not just try it yourself and see if they change?

[Matt Clark]

32gb USB to USB across a VM.... :'(

[Ƭᴇcʜιᴇ007]

If you just want to test if DD changes UUID's or not, then why not just use a small test source disk/partition with little data on it, locally?

[Matt Clark]

And the last part is still valid. If the UUID stays the same, how the the system deal with multiple of the same UUID? I guess that works...

[Ƭᴇcʜιᴇ007]

Related: askubuntu.com/questions/156063/…

[Matt Clark]

I failed to find this in my initial search. Found my answer, and I appreciate the help.

[Admin]

"However booting and mounting a device by UUID will become ambiguous and may lead to the wrong device being used." Yes. This can become really dangerous when a cloned disk is used as backup. You need to double check that /home is really the disk you think it is. A "backup" done in the wrong direction can wipe out data from both disks.